Aerators are commonly used for maintaining landscaped ground surfaces including turf. The term “turf” refers to grass and other material which is specifically grown for sporting activities and is used, for example, to form golf course greens. Aerators on these types of surfaces have tines that repeatedly penetrate the ground surface, forming a plurality of holes so that the ground surface is aerated, to improve growth of the grass or other material and enhance the condition of the surface for playing purposes.
In conducting this type of aeration of turf surfaces, the neatness of the holes made by the aerator tines can significantly affect the overall result. For example, in the case of golf greens and the like where the vegetation is short, a hole with rough edges or too large a hole can cause spot erosion, resulting in an undesirable dimple in the ground surface. This effect is aggravated when forward movement of the aerator differs from the speed of the coring head over the ground surface, causing the tines to rake across or break the ground surface.
To minimize rough edges of the holes, aerators may be designed to keep the tines substantially vertical for entry and withdrawal from horizontal ground surfaces. For example, aerators may have flywheels that drive the upper ends of tine supports in a circular path, and the lower ends in a reciprocating motion of repeated penetrations into the ground. Link arms can pivot to compensate for forward motion of the machine. At each part of the cycle when the tines are withdrawn from the ground surface, the link arms may position the tines in a substantially vertical position for the next cycle of penetration into the ground. Tines are generally cylindrical and produce holes by pulling up plugs or cylindrical cores of soil as the tines move by rotation of the flywheel.
Holes produced by aerator tines may be substantially vertical, and perpendicular to ground surfaces, when ground surfaces are horizontal. However, the holes may not be perpendicular to undulating or sloped surfaces. For example, golf courses may have undulations or steep slopes in need of aeration. While an aerator travels over undulations or slopes, the coring head may not be perpendicular to the ground surface and, as a result, the tines may enter and/or exit the ground at angles that are not perpendicular to the ground surface. As a result, the holes are not perpendicular to the ground surface, and may have rough edges and be subject to erosion. Additionally, if the tines are not perpendicular to the ground surface, they do not provide uniform hole depth. Nor do the tines provide uniform spacing between the holes.
The problem of tines that are not perpendicular to the ground surface also may be due to wider coring heads that are positioned rearwardly of the axle of the supporting wheels. If a coring head is mounted behind the supporting axle of the aerator, and the aerator's wheels ride over a rise in ground contour before the tines fully penetrate the ground, the holes will have a reduced depth. Conversely, if the wheels ride over a dip as the tines penetrate the ground, the tines will produce deeper holes.
U.S. Pat. No. 7,293,612 relates to a Walk Aerator with Ground Following Coring Head designed to adjust the vertical position of the coring head relative to the frame in response to changes in ground contour. If the skid assembly rotates sufficiently out of its horizontal position, a pivotal connecting rod attached to the skid assembly causes a switch actuator to depress either of a pair of limit switches. Each limit switch may actuate a hydraulic cylinder to raise or lower the height of the coring head on the frame. As the coring head moves up or down, however, the tines may not be perpendicular to the ground surface.
An aerator is needed that can produce holes that are perpendicular to undulating or sloped ground surfaces, and that have uniform depth and spacing.